The present invention broadly relates to semiconductor processing equipment, and deals more particularly with a robotic system for transporting semiconductor wafers between any of a plurality of processing stations.
The need for increasing yield and through-put in semiconductor manufacturing systems has resulted in the development of highly specialized and automated systems for processing and handling semiconductor wafers. Wafers are typically stored in a cassette with their flat surfaces horizontal. The cassettes are transferred from station to station by automatic material handling equipment. Once delivered to a processing station, individual wafers are transferred from the cassette by an automatically controlled robot that typically includes a robotic arm carrying a wafer supporting blade on its outer end. The blade is moved in a manner to pick up individual wafers such that the wafer lays flat on the blade during the transfer process. This arrangement has the advantage that a wafer is held on the end of the robotic arm through force of gravity, thus avoiding the application of unnecessary or unbalanced forces to the wafer that could result in damage to the wafer. In spite of the fact that the robotic arm for transferring the wafers is automatically controlled, slight misadjustments, errors caused by wear and software xe2x80x9cglitchesxe2x80x9d can result in problems during the wafer transfer process. For example, in some cases, misalignment of certain components in the system, such as the blade, robotic arm or the cassette, can result in a wafer being loaded onto a blade such that the wafer is tilted relative to the blade, i.e., not horizontal on the blade. In other cases, although the wafer may be supported flat on the blade, the blade itself may be tilted before it lifts a wafer from the cassette. In still other cases, where the rotational position of the robotic arm relative to a cassette is not precisely indexed or where the blade is tilted out of its normal horizontal position, attempts to fetch a wafer from the cassette may result in the robotic arm or the blade colliding with a door-slit insert of the load lock chamber which in turn results in damaging or breaking the wafer. Even where the robot succeeds in lifting the wafer from the cassette, alignment errors in the transfer process can result in collisions between the process chamber pedestal, slit door, lower parts of the chamber and the wafer direct loading, unloading or transfer of the wafers.
The problem described above involving wafer damage due to errors in the transfer process have become more significant as the size of the wafer continues to grow, along with advances in wafer processing technology. This type of wafer damage reduces throughput and process yield, and is becoming more costly due to the larger size of wafers.
One partial solution to the above discussed problem is a so-called orienter chamber in which the robot transfers the wafer to a chamber whose sole purpose is to determine whether the wafer is properly positioned on the blade and then manipulate the wafer so that it is properly oriented on the blade before the wafer is transferred to other processing chambers. While the use of an orienter chamber has somewhat reduced wafer damage due to misalignment, this technique reduces throughput since valuable time is lost in transferring the wafer to and from the orienter chamber.
The present invention is directed toward overcoming the deficiencies of the prior art wafer transfer systems described above.
According to one aspect of the invention, apparatus is provided for holding and transferring a semiconductor wafer, comprising a robotic arm for transferring the wafer, a blade attached to a robotic arm for supporting and holding the wafer, clamping means for both moving the wafer into a desired, aligned, position and then clamping the wafer on the blade, and means for driving the clamping means between a retracted position and a closed, clamping position. The clamping means preferably comprises four clamping members respectively mounted on the corners of the blade which are normally spring biased to their open or retracted position. The clamping members are connected to a central hub that is rotatively mounted on the bottom of the blade and is driven to rotate by movement of the robotic arms. Each of the clamps includes a first, beveled surface that functions to engage the outer periphery of the wafer and move it into proper alignment, and a second, clamping surface that overlies the top of the wafer to hold on the blade in a properly aligned position. In the preferred embodiment, a laser detection system is employed to determine when the wafer is mis-aligned or xe2x80x9ctiltedxe2x80x9d on the blade. If the wafer is not too far out of alignment, the clamping system is activated to move the wafer into proper position. Otherwise, the wafer transport sequence is interrupted to await manual intervention in order to correct the alignment problem.
In accordance with another aspect of the invention, apparatus is provided for holding and transporting a semiconductor wafer comprising a blade for supporting a wafer, a plurality of guide clamps reciprocally mounted on the blade at locations around the periphery of the wafer, and means for moving the guide clamps into engagement with the wafer in order to move the wafer to a desired, aligned position on the blade.
Accordingly, it is a primary object of the present invention to provide apparatus for transporting semiconductor wafers which assures that the wafers are held in proper alignment during the transfer process.
Another object of the invention is to provide apparatus as described above which eliminates the need for a dedicated chamber heretofore necessary for re-orienting the wafer so as to be properly aligned on the blade.
Another object of the invention is to provide apparatus of the type mentioned that permits wafer misalignment to be quickly corrected while also reducing the possibility that the wafer is scratched, dropped, or otherwise damaged during the re-alignment process.
A further object of the invention is to provide apparatus as described above which significantly increases the overall wafer transfer speed, and thus the throughput in the semiconductor manufacturing process.
These and further objects and advantages invention will be made clear or become apparent during the course of the following description of a preferred embodiment of the invention.